Which is exactly what I'd do. I've got the brick and whenever I need to heat a large object it gets surrounded with the brick and out comes the rosebud. But I think that the weed burner may actually put out more BTUs than the small rosebud. It really cranks! My Dad got one and was shocked at how much heat it put out. It sucks down a 20 pound bottle pretty fast. In fact, in cooler weather the output drops because the propane becomes too chilled. ERS
The weed burners work well enough for a forge burner, but it's a good idea to mount them so there's an inch or so gap between the burner shroud and the bricks to avoid burning up the shroud. Many of them only have a sheet metal cover. As long as the flame gets inside the chamber, such an arrangement should easily reach a welding heat.
My 22" X 10" dia tubular forge uses two burners I made of 3/4" black pipe with 2" X 3/4" reducing bells for air intakes. The orifices are set into the sides of 3/8" pipe tapped M6X1 and welded across the bells. I use .030 MIG gun tips for orifices.
So far, the burner tubes show no objectionable erosion after 5 years.
With 2" of Kaowool liner, I can reach welding heat in about 10 minutes at 15 psi propane pressure. General forging heat is obtainable at 5 psi with little scaling. Sometimes it's better to restrict air at such low gas pressures, but I've heard felllows claim forging heat at 1-2 psi. No idea of the orifice sizes they use though.
HTH
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